Flap as animal trapped between lines (5)
I believe the answer is:
lapel
'flap' is the definition.
(I know that lapel is a type of lap)
'animal trapped between lines' is the wordplay.
'animal' becomes 'ape' (ape is a kind of animal).
'trapped between' is an insertion indicator.
'lines' becomes 'll' (two abbreviations for line).
'ape' inserted inside 'll' is 'LAPEL'.
'as' is the link.
(Other definitions for lapel that I've seen before include "top of coat" , "Part of a folded back collar" , "Part of a suit jacket" , "Turned-back part of coat collar" , "Extended part of a collar" .)